Heat 6 tablespoons of olive oil in a soup pot over low heat. Add 1 thinly sliced large onion, 2 thinly sliced medium ribs of celery and 8 cloves of peeled and smashed garlic to the pot, and cook until soft. Add 1/3 cup of white wine, 2 tablespoons of tomato paste, 3 pinches of saffron threads and 8 cups of fish and/or shrimp stock to the pot. Also add 1/4 teaspoon crushed red pepper flakes, the juice of 1 orange and two 3-inch strips of orange zest to the pot. Bring to a simmer, then cook uncovered for about 45 minutes until the liquid reduces by one-third.

Cut 2 fennel bulbs crosswise into 1/3-inch slices, and add to the pot with 3/4 cup of peeled, seeded and chopped fresh tomatoes. Cook for about 20 minutes, until the fennel becomes soft. Season the soup to taste with salt and freshly ground black pepper, then season 1 1/2 pounds of firm white fish fillets with salt and pepper. Cut the fish into 1 1/2-inch chunks, then add to the pot with 1 pound of peeled and deveined shrimp and 1 tablespoon of chopped fresh parsley leaves. Cook for about five minutes, stirring gently only a couple times. Serve in a shallow bowl with garlic-rubbed croutons.